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OPTICAL TRACKING

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... are imaged by high speed digital cameras. The number of the cameras depends on the type of motion ... Facial motion capture usually uses one or two cameras. ... – PowerPoint PPT presentation

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Title: OPTICAL TRACKING


1
OPTICAL TRACKING
  • Mithat Daglar


    Ltjg.

2
Presentation Outline
  • Overview
  • How they work
  • Advantages
  • Disadvantages
  • Eye Tracking
  • Links

3
Overview
  • The mostly used trackers use magnetic field. The
    biggest problem with the magnetic trackers is
    their limited range. As the range increases so
    the possibility of distortion is also increases.
    They are also very too much sensitive to the
    environment. Metals and electromagnetic
    interference cause distortion in the result.
  • The optical trackers are used to overcome these
    limitations.

4
Overview
  • Optical trackers are mainly used for two
    purposes in computer applications
  • For computer animation (human movement analysis)
  • Virtual environment (to capture the precise
    information about the position and the
    orientation of the users head)
  • Early examples of optical trackers, such as
    Op-Eye and SelSpot were used by MIT and New York
    Institute of Technology in 1982-1983.

5
How They Work
  • Optical tracker systems use either reflective or
    IR-emitting markers and video cameras to monitor
    the tracking space.
  • For body motion analyze 20 - 30 markers are
    attached to the body (especially to the joints).
    Number of the markers depends on the the desired
    resolution. More markers give more accurate
    results.
  • The markers are small spheres or disks covered in
    reflective material. Can be distinguished by
    their shape, brightness and size.

6
How They Work
7
How They Work
8
How They Work
9
How They Work
  • The markers are imaged by high speed digital
    cameras. The number of the cameras depends on
    the type of motion capture.
  • Facial motion capture usually uses one or two
    cameras. Full body motion capture may use four
    to six cameras to provide full coverage of the
    active area.
  • To enhance contrast, each camera is equipped
    with IR-emitting LED

10
How They Work
  • IR pass filters are placed over the camera
    lenses.
  • Cameras are attached to the controller cards,
    typically in a PC chassis.
  • Before motion capture begins, a calibration
    frame -a carefully measured 3D array of markers-
    is recorded. This defines the frame of reference
    for the motion capture session

11
How They Work
  • During the motion capture session, the computer
    is presented with each camera view.
  • After the motion capture session, the recorded
    2D motion data is converted to 3D position data
    by using triangulation approach.
  • This resultant data is typically applied to an
    inverse kinematics system, to animate a skeleton.

12
How They Work
  • Actions
  • Chutes
  • Courses
  • Face
  • Expressions
  • Combats
  • Sports
  • Extra

13
How They Work (wide area tracking)
  • In a virtual environment, to provide the user
    with the impression of being immerse in the
    simulated 3D environment, precise information
    about the user s head is required.
  • For this purpose, another optical tracking system
    is used and is called Wide Area Tracking.
  • This system uses ceiling panels housing LEDs, a
    miniature camera cluster called HiBall and a
    single-constraint-at-a-time (SCAAT) algorithm
    which converts individual LED position into
    position and orientation data.

14
How They Work (wide area tracking)
  • Ceiling
  • Current applications cover up to 4,000 cubic
    feet.(500 sequare feet X 8 feet). But can be
    easily expanded by adding new tiles.

15
How They Work (wide area tracking)
  • HiBall

16
How They Work (wide area tracking)
  • HiBall is a cluster of 6 lenses and 6
    photo diodes
    arranged so that each
    photo diode can view LEDs
    thorough
    several lenses.
  • SCATT algorithm computes the position
    of the user by using
    the LED sightings
    provided by HiBall.

17
Advantages (Optical Body Motion Tracking)
  • Large Possible Active Area Unlike magnetic
    tracking system, depending on the system used and
    the precision required, the motion capture area
    can be arbitrarily large.
  • Unencumbered Subject The subject is not
    physically attached to the tracking system.
  • Markers are passive Since markers are the
    active elements of the system, additional markers
    cost very little. Hundreds of markers can be
    used for a motion track.

18
Advantages (Optical Body Motion Tracking)
  • High enough sampling rate for most sport moves
    At 120 to 200 Hz sampling rate, most human
    motions are easily measured.
  • Free from electromagnetic interference.

19
Disadvantages (Optical Body Motion Tracking)
  • Cost Most expensive tracking systems.
  • Bioengineering Technology Systems (Superfluo)
    Uses passive markers. 135,600 (50Hz) 33,000
    (for upgrade to100Hz)
  • Selspot AB(Selspot II) IR LEDs - 37,000
  • Northern Digital (Optorack) IR LEDs - 80,000
  • Motion Analysis Corp (Expert Vision 3D) 38,
    500

20
Disadvantages (Optical Body Motion Tracking)
  • Sensitivity to light Background, clothing,
    ambient illumination effect the accuracy.
  • Sensitivity to reflection Wet or shiny
    surfaces (mirrors, floors, jewelry, and so on)
    can cause false marker readings.
  • Marker Occlusion Since a marker must be seen
    by at least two cameras (for 3D data), the
    occlusion caused by subject (human), materials
    in the environment and the other markers can
    result in lost, noisy, displaced or swapped
    markers.

21
Disadvantages (Optical Body Motion Tracking)
  • Tracking time Tracking time can be much greater
    than the actual capture session and may vary
    unpredictably, depending on accuracy
    requirements, motion difficulty, and the quality
    of the raw data captured.
  • Non real-time device Since there is no
    immediate feedback , it is impossible to know if
    a motion is adequately captured. More than two
    sessions may be needed.
  • Sensitivity to calibration Since multiple
    cameras, the frame of reference for each camera
    must be accurately measured.

22
Eye Tracking
  • Are similar to optical trackers. Using infrared
    illumination and lightweight high-resolution
    video sensors.
  • The IR waves created by IR LEDs are reflected by
    the eye. This reflection is captured by video
    sensors and white and black colors are used to
    calculate the position of the pupil.

23
Eye Tracking(SensoMotoric Instruments products)
  • Headband/Helmet-mounted Eye tracking Device
  • Can record eye movement with unrestricted head
    movement

24
Eye Tracking(SensoMotoric Instruments products)
  • Remote Eye tracking Device (R.E.D.)
  • Eye movements can be acquired without physical
    contact to the subject.
  • The R.E.D., placed in front of the subject
    below the line of sight, automatically tracks
    the subject¹s eye within the range of natural
    head movements.

25
Eye Tracking(SensoMotoric Instruments products)
  • Head Mounted Display with integrated eye
    tracking (H.M.D.)
  • Integrated with Head-mounted display (HDM).
    Useful for virtual reality applications.

26
Eye Tracking(Quick Glance)
  • Consists of two IR LEDs and a camera
  • The camera and light sources are
    mounted on the
    computer's monitor.
  • Examines the reflections from the user's eye
    which is illuminated by LEDs . The reflected
    light is focused onto the camera. By analyzing
    the position of the light reflections and the
    center of the pupil contained in the image, the
    gaze point is determined. Duration can also be
    derived. With that information, the software
    controls the location of the cursor according to
    the gaze point and its duration.

27
Eye Tracking(ISCAN)
28
Links
  • Optical Tracking
  • http//www.cs.unc.edu/tracker
  • http//www.ndigital.com
  • http//www.peakperform.com
  • http//www.motionanaliysis.com
  • http//www.actisystem.fr
  • Eye Tracking
  • http//www.smi.de/iv/index.html
  • http//www.gkc.co.uk/vr-systems/borgtext.htm
  • http//www.dinf.org
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